A radio access scheme and a radio network of cellular mobile communication (hereinafter, referred to as “Long Term Evolution (LTE)” or “Evolved Universal Terrestrial Radio Access: EUTRA”) have been studied in the 3rd Generation Partnership Project (3GPP). In the LTE, a base station device (base station) is also referred to as an eNodeB (evolved NodeB) and a terminal device (mobile station, mobile station device, terminal) is also referred to as UE (User Equipment). The LTE is a cellular communication system in which a plurality of areas covered by base station devices are arranged in a cell-like shape. A single base station device may manage a plurality of cells.
The LTE is ready for Frequency Division Duplex (FDD) and Time Division Duplex (TDD). The LTE employing a FDD scheme is also referred to as FD-LTE or LTE FDD. The TDD is a technique that allows full-duplex communication in at least two frequency bands by performing frequency-division multiplexing of an uplink signal and a downlink signal. The LTE employing a TDD scheme is also referred to as TD-LTE or LTE TDD. The TDD is a technique that allows full-duplex communication in a single frequency band by performing time-division multiplexing of an uplink signal and a downlink signal. Details of the FD-LTE and the TD-LTE are disclosed in NPL 1.
A base station device is able to transmit, to a terminal device, a reference signal (also referred to as RS) which is a known signal between the base station device and the terminal device. A plurality of reference signals may be transmitted for various purposes such as demodulation of a signal and a channel and reporting of a channel state. For example, a cell-specific reference signal is transmitted in all downlink subframes as a reference signal specific to a cell. In addition, for example, a terminal-specific reference signal is transmitted as a reference signal specific to a terminal device in a resource in which a data signal to the terminal device is mapped. Details of the reference signals are disclosed in NPL 1.
In the 3GPP, introduction of a small cell has been studied. A small cell is a collective term indicating a cell in which transmit power of a base station device forming the cell is small and which has smaller coverage than that of a conventional cell (macro cell). For example, when small cells are applied with a high frequency band, it is possible to arrange the small cells at high density and an effect of improving spectral efficiency per area is achieved. In the study of introduction of a small cell, discussion on a technique of switching the base station device to a stop state for various purposes such as reduction in power consumption and reduction in inter-cell interference has been carried out. Details thereof are disclosed in NPL 2.